This invention generally relates to discharge devices and, more particularly, to so-called metal halide discharge devices wherein alkali metal halide and scandium halide is used in predetermined proportions and in predetermined amount to enhance the device efficacy.
In U.S. Pat. No. 3,234,421 dated Feb. 8, 1966, is disclosed a so-called metal halide discharge lamp wherein selected metal halides, and particularly those of Group IA, IIA, IIB and IIIA, are incorporated into the device in order to modify the color of the discharge and the operating efficacy of same with respect to the generation of visible light.
In U.S. Pat. No. 3,407,327 dated Oct. 22, 1968, is disclosed a high-pressure discharge device which contains mercury, halogen, scandium and alkali metal. The dosings or loadings of sodium iodide and scandium iodide in the arc tube envelope, when calculated on a gram molecular basis, overlap at their extremes although normally, the grams moles of sodium halide greatly exceed the gram moles of scandium halide as utilized in this device. In the preferred specific example which is recited at column 5, lines 28-32 of this patent, sodium iodide is utilized in amount of 19 milligrams, thorium in amount of 0.5 milligram, and scandium metal, some of which later converts to the iodide, is dosed into the arc tube in amount of 0.5 milligram. The resulting molecular ratio of sodium iodide to scandium is in excess of approximately 11.5:1, which greatly exceeds the molecular ratios desired for these respective materials if best efficacy is to be obtained, as will be explained hereinafter.
In U.S. Pat. No. 3,786,297 dated Jan. 15, 1974, is disclosed still another modification for a metal halide discharge device wherein cerium and cesium halides are utilized with a high mercury loading in order to obtain a very efficient discharge with a relatively low minimum envelope temperature. In the preferred embodiment as disclosed in this patent, alkali metal iodides and rare-earth metal iodides are used in about equal gram-mole proportions. It is also known to use alkali metal halides and rare-earth metal halides including scandium halides and yttrium halides in equal gram-molar proportions.
Many other modified metal-halide HID devices are disclosed in the patent and other literature. These devices generally will display an improved operating efficacy as compared to the standard high-pressure mercury-discharge device as well as improved color, both from the aspect of the appearance of the light source as viewed directly and with respect to the color rendering of objects which are illuminated by the devices.